Light + nitrogen = green
First look at the source of nitrogen, for it could be ammonia (terrible!), nitrites (very bad!), or nitrates (still bad!).
It could be lack of filtration from dirty filter, undersized filter, crashed filter from meds or low pH.
Or it could be ammonia from improper water treatment, as in if you had chloramine and used a water treatment that says "treats chloramine and chlorine" but does not also say "treats ammonia". In any case, green water or green algae is your friend in that it uses the products that otherwise could harm your fish.
Please do water tests for ammonia, nitrite, nitrate, as well as pH and share that data with us.
Then work on reducing the lighting, but realize that the green is telling you you have a nitrigen probelm, if you cut off the light without addressing that issue the fish will suffer.